It may not be the worst advice but it's not good advice. I don't think people freeze in an attack because they're carefully considering the legal ramifications of their actions. I don't recommend anyone hesitate to react. I'm just saying going to prison shouldn't be considered an option. Life in prison can be considered a fate worse than death for some, either way you're not much use to your family.It's certainly not the worst advice and certainly no one has come up with anything else that can convey in such a memorable way that you have to do what you must to survive an attack and which will come back to you at the vital moment you need it to!
it's a cliché certainly but the worst thing someone can overdo is falter because they are overthinking what they'd been told to do in such a situation. If you start the 'what if' thing while being attacked (what if I hit him and he falls hits his head and dies........what if I push him and he falls into the road and gets run over....etc etc etc) then you are doomed to be beaten up or worse so a little mantra that says better to be tried by 12 etc is not the worse thing you can think. Unless you are a seasoned 'street fighter' who fights nightly or weekly and have the instincts of Batman so that you need no prompting to defend yourself, it's a useful reminder. People really do freeze in an attack, even martial artists, I've seen it.
For example, I've trained in a class where the technique had you disarming an attacker, throwing him to the ground than stabbing the downed opponent. The technique might be appropriate on a battlefield but the scenario would have very limited situations where it could legally be applied to reality for most people. If someone walks up and sees you stabbing a downed opponent you're asking for trouble. This is the mentality some have when it comes to survive at all costs. Stabbing a downed opponent is not a good idea.